The present invention relates to a method of ion plantation, and especially to a method for forming an ultra-shallow junction by boron plasma doping.
With the progress of semiconductor elements, the manufacturing of semiconductor elements are more and more precise and therefore, the depth distribution of impurity atoms are more and more precise. In general, an ion planting method is used to precisely control the depth and concentration distributions of impurity atoms. In the process of ion planting, the impurity atoms with a form of charged ions are accelerated to have an energy and then they can collide the silicon wafer directly to enter into a proper position in the crystal lattices. Therefore, the depth distribution of the ions can be controlled by the energy of the ion, while the dose of the impurity atoms can be controlled by the planting time and current of the ion beam.
In the prior art, the charged ions as an ion beam with certain energy is planted into a silicon wafer by using an ion planter. Then, a thermal processing is used to repair the damage due to ion planting and thus, a required electric active function is achieved. In order to suppress a short channel effect, the angle between a chip and an incident ion beam must be adjusted properly. In general, the tilt angle used is about 7 degrees, and the chip is a specific twist angle for increasing the possibility of collision of the ion beam and silicon atoms. This way of injecting the ion beams one by one need a longer time and ions can not be uniformly distributed on the wafer, moreover, the tilt angle of the wafer must be controlled precisely. Moreover, when the line width of the device is required to be reduced to be below 0.18 xcexcm , and area of each section, including source and drain, in the metal oxide semiconductor (MOS) must also be reduced, and thus the diffusing depth of the junction must be controlled severely for reducing the short channel effect and the punch-through effect. Therefore, an ion doping with a further lower energy and a rapider thermal process are used. However, when the energy of ion-planting is lower than 1 KeV, the ion current will be over-low, and thus the product will be reduced greatly. As a consequent, the trend of increasing the product in unit dustless area can not be performed. Furthermore, due to the reduction of areas of semiconductor elements, the electricity for planting ion pair elements to a wafer opaquely will be affected greatly. Further, since a lower energy and high does ion plantation, the amorphous ion plantation can not acquire an effect of shallow plantation to the ion energy ion plantation. On the contrary, one more manufacturing process will reduce the amount of products so that the aforesaid method can not meet a manufacturing process below 0.1 xcexcm.
Therefore, the object of the present invention is to disclose a method for manufacturing an ultra-shallow junction so as to resolve the aforesaid problem.
Accordingly, the primary object of the present invention is to provide a method for forming an ultra-shallow junction by boron plasma doping for acquiring a flat and uniform ultra-shallow junction. Therefore, after the next thermal process, the property of the element can be retained. A lower depth junction is acquired, and the diffusion in the horizontal direction is suppressed.
Another object of the present invention is to provide a method for forming an ultra-shallow junction by boron plasma doping, wherein boron ions is completely near the surface of the wafer substrate. The damage to the wafer substrate is reduced. This is beneficial to the re-crystallization in the thermal process.
According to the present invention, a substrate is placed in a pulse type electric field. A flowing carrying gas drives boron ions in a channel above the substrate, and then a negative pulse type voltage is applied so that the boron ions may uniformly enter into the substrate. Then a rapid annealing process is performed so as to be formed with an ultra-shallow junction on the substrate.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing.